Water, Phosphine, and the possibility of life elsewhere in the Solar System

Young Astronomers Blog, Volume 28, Number 20.

Although many have dreamed about life on other worlds, so far, life has only been found on the Earth.

The search for life has gone down one avenue as new “exoplanets” are found and we get closer to finding a planet like the Earth orbiting another star. This will involve discoveries by the Transiting Exoplanet Survey Satellite (TESS) along with the James Webb Space Telescope (JWST). More on this later, once the JWST launches in late 2021.

Another avenue has been what NASA calls, “follow the water”, and scientists have found plenty of water in the outer part of the Solar System. However, much of it is frozen as ice.

This first brings us to Mars. Scientists think that Mars was warmer and wetter in the distant past and it is thought that Mars still has a significant amount of water ice beneath its surface. Although life might not exist today on Mars, liquid water could have been plentiful a few billion years ago creating conditions sufficient for life to exist.

In 2018 and again in September 2020, scientists discovered evidence for underground liquid water under the ice at the southern pole of Mars.

Many of the moons in the outer part of the Solar System are covered with water ice. The real surprise is that scientists have found liquid water beneath the surface of several moons. And the thought is, if there is liquid water, could there be life? Two of the most promising candidates are Jupiter’s moon Europa and Saturn’s moon Enceladus. Both are believed to have underground oceans beneath their surfaces. In fact, Enceladus has icy geysers erupting from four “tiger stripes” at its south pole. Just recently, scientists published some images of Enceladus showing that, in addition to the activity at its southern pole, there is some geological activity in Enceladus’ northern hemisphere as well.

Titan is probably the most interesting moon in the solar system. It also has an underground ocean of liquid water. But in addition, it has a thick atmosphere composed mostly of nitrogen like the Earth. However, there is methane rather than oxygen in the atmosphere. It is so cold on Titan that water is frozen as rock hard ice on its surface. Methane, although a gas on Earth, exists as a liquid on Titan filling lakes and seas at Titan’s northern and southern poles. This makes Titan the only object in the Solar System other than the Earth with a nitrogen atmosphere and with liquid flowing on its surface.

A third avenue appeared just recently. There have been past studies postulating that if life were found on Venus, it would be in the clouds. The temperature on the surface of Venus is around 880^o F, with a pressure 90 times that of the Earth at sea level. However, it is relatively temperate some thirty miles up in the atmosphere.

In September 2020, scientists discovered a chemical called phosphine (PH₃) in the clouds of Venus. The interesting thing is that phosphine is difficult to make without life. On Earth, it is a smelly and poisonous gas produced by microbes in a non-oxygen environment.

Phosphine was first detected using the James Clerk Maxwell Telescope (JCMT) in Hawaii and later confirmed with the Atacama Large Millimeter/submillimeter Array (ALAM) in Chile. In both cases, they observed a dip in the spectrum of “radio light” at the wavelength absorbed by phosphine.

This discovery did not directly find life, just a chemical that could be produced by life. Although some scientists are skeptical, this could add Venus to the list of planets and moons other than the Earth that have a potential for life. For now, we will wait for the next space mission to explore Venus to find out more.

After the initial fanfare about the potential of phosphine in Venus’ atmosphere, and the posting of this article, additional studies have cast doubt on the finding. The scientist who announced the original discovery have downgraded their estimate on the amount of phosphine detected in the atmosphere of Venus. Another study attributed the finding to sulfur dioxide (SO2) and not potential microbial life.

In the fall of 2022, the flying observatory SOFIA (Stratospheric Observatory for Infrared Astronomy) failed to detect phosphine in Venus’s atmosphere. However, Jane Greaves and the original team challenged this result, so the debate goes on.

Selected Sources and Further Reading

“Planets.” NASA Science, Solar System Exploration. (accessed September 23, 2020). https://solarsystem.nasa.gov/planets/overview/

Gareth Dorrian. “The four most promising worlds for alien life in the solar system.” The Conversation. September 18, 2020. https://theconversation.com/the-four-most-promising-worlds-for-alien-life-in-the-solar-system-146358

“Ocean Worlds, Water in the Solar System and Beyond.” NASA. (accessed September 23, 2020). https://www.nasa.gov/specials/ocean-worlds/#rosetta

“Ocean Worlds Infographic.” NASA Science, Solar System Exploration. Source: NASA/JPL-Caltech/Kim Orr. April 20, 2017. https://solarsystem.nasa.gov/resources/16179/ocean-worlds-infographic/

Charles Q. Chol. “Water on Mars: The Story So Far.” Astrobiology at NASA, Life in the Universe. October 14, 2016. https://astrobiology.nasa.gov/news/water-on-mars-the-story-so-far/

Jay Bennett. “Underground Lake of Liquid Water Detected on Mars. ”Popular Mechanics. July 25, 2018. https://www.popularmechanics.com/space/moon-mars/a22541370/underground-lake-liquid-water-mars/

Siladitya Ray. “New Evidence of Underground Saltwater Bodies Raise Possibility Of Life On Mars.” Forbes. September 29, 2020. https://www.forbes.com/sites/siladityaray/2020/09/29/new-evidence-of-underground-saltwater-bodies-raise-possibility-of-life-on-mars/#76e3c23333ce

“Infrared Eyes on Enceladus: Hints of Fresh Ice in Northern Hemisphere.” NASA/JPL-Caltech. September 18, 2020. Image Credit: NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science Institute. https://www.jpl.nasa.gov/news/news.php?feature=7748

“Hints of life on Venus.” Royal Astronomical Society. September 14, 2020. https://ras.ac.uk/news-and-press/news/hints-life-venus

Mark Zastrow. “Astronomers spy phosphine on Venus, A potential sign of life.” Astronomy. September 17, 2020. https://astronomy.com/news/2020/09/astronomers-spy-phosphine-on-venus-a-potential-sign-of-life

“RAS Press Briefing – Phosphine of Venus.” Royal Astronomical Society/YouTube. September 14, 2020. https://www.youtube.com/watch?time_continue=5&v=y1u-jlf_Olo&feature=emb_logo

Adam Mann. “’Grand claims’ of life on Venus lack evidence, skeptics say.” Live Science. September 22, 2020. https://www.livescience.com/skepticism-life-on-venus.html

Matt Williams. “Scientists Have Re-Analyzed Their Data and Still See a Signal of Phosphine at Venus. Just Less of it.” Universe Today. November 20, 2020. https://www.universetoday.com/148865/scientists-have-re-analyzed-their-data-and-still-see-a-signal-of-phosphine-at-venus-just-less-of-it/

Eric Betz. “Life in the clouds of Venus? Maybe not.” Astronomy. February 3, 2021. https://astronomy.com/news/2021/02/life-in-the-clouds-of-venus-maybe-not

Nancy Atkinson. “SOFIA Fails to Find Phosphine in the Atmosphere of Venus, But the Debate Continues.” Universe Today. December 5, 2022. https://www.universetoday.com/158983/sofia-fails-to-find-phosphine-in-the-atmosphere-of-venus-but-the-debate-continues/

Technical Reading

Lauro, S.E., Pettinelli, E., Caprarelli, G. et al. “Multiple subglacial water bodies below the south pole of Mars unveiled by new MARSIS data.” Nature Astronomy. September 28, 2020. https://www.nature.com/articles/s41550-020-1200-6

Greaves, J. S., Richards, A. M. S., Bains, W. et al. “Phosphine gas in the cloud decks of Venus.” Nature Astronomy. September 14, 2020. https://www.nature.com/articles/s41550-020-1174-4 & https://www.nature.com/articles/s41550-020-1174-4.pdf

Andrew P. Lincowski, et al. “Claimed detection PH₃ in the clouds of Venus is consistent with mesospheric SO₂.” January 25, 2021. https://arxiv.org/abs/2101.09837

Jane S. Greaves, Anita M. S. Richards, William Bains, et al. “Re-analysis of Phosphine in Venus’ Clouds.” December 10, 2020. https://arxiv.org/abs/2011.08176 &  https://arxiv.org/ftp/arxiv/papers/2011/2011.08176.pdf

M. A. Cordiner, et al. “Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations.” October 24, 2022. https://arxiv.org/abs/2210.13519

Jane S. Greaves, et al., Recovery of Phosphine in Venus’ Atmosphere from SOFIA Observations. November 17, 2022. https://arxiv.org/abs/2211.09852

Harold Morowitz & Carl Sagan. “Life in the Clouds of Venus?” Nature. Volume 215. Pages 1259-1260. September 16, 1967. https://www.nature.com/articles/2151259a0